Anchor bolts and method for fixing same in drill holes especially in friable rock



j FIGB d v b c INVENTOR S R. NOVOTNY ET AL ESPECIALLY IN FRIABLE ROCK FileiOct. 3l, 1966 March 4, 1969 ANCHDR Bours AND METHOD FDR FIXING SAME 1N DRILL HoLEs f A A .D C L A.

United States Patent O 3,430,449 ANCHOR BOLTS AND METHOD FOR FIXING SAME IN DRILL HLES ESPECIALLY IN FRIABLE ROCK Rudolf Novotny, 22 Ostpreussenstr., 43 Essen, Germany,

and Fritz Schuermann, 8 Am Kronenberg, 4321 Winz- Niederwenigern, Germany Filed Oct. 31, 1966, Ser. No. 590,629 Claims priority, application Germany, Nov. 27, 1965,

B 84,734 U.S. Cl. 61-45 2 Claims Int. Cl. E21d 20/00, 21/00; F16b 13/06 ABSTRACT F THE DISCLOSURE The method of fixing an anchor bolt in a drill hole, especially in friable rock, by means of a mixture of polyester resin with a viscosity of the order of lO poises with a finely granulated filler in an amount in the ratio of the order of 100 to 400% of the weight of the resin and a hardener, placed in the drill hole, the anchor bolt being smooth and there being an annular clearance between the anchor bolt and the drill hole of the order of 1.5 mm. The drill hole is closed at its outer end by the conformation of the anchor bolt. 'Positioning of the anchor bolt is effected at a rotational speed of the order of 150 to 750 rpm. and at a mechanically exerted pressure of about 900 kg. An anchor bolt of elongate tubular form filled with stiffenable material and with an exterior smooth form and having a conically thickened head closing the outer end.

The invention relates to a method for fixing anchor bolts in drill holes, especially in friable rock, by means of a supply (positioned in the furthest part of the drill hole in a cartridge destroyed by the insertion of the anchor bolt) of a mixture of a plastic with a filler and an accelerator on the one hand and a hardener on the other hand, in separate compartments.

In methods of this type the aim is the attainment of maximum utilization of the inserted material and, on the other hand, the achieving of adequate safety in the rock, that is, the binding together of as much as possible of the layer of rock penetrated by the drill holes.

For this purpose the procedure is already known of bracing against the rock expanding anchors or anchors fastened at the furthest part of the drill hole according to the principle of the adherent anchor process with the aid of plastics having the composition described in the opening passage, the bracing being by means of clamping plates or the like placed on the free ends projecting from the drill hole. This method, which has proved itself effective for consolidating mine workings located in good rock, is not, however, suited to friable rock, because the stability of the drill hole walls is inadequate to form a buttress for the bracing action.

Further, the procedure is already known of employing adherent anchors with plastic material and bolts with cement but having no supporting plate, the cement and plastic penetrating into the loose places in the rock and thus cementing the stony mass together and so reinforcing it. With cement the disadvantage arises that this material later breaks away from the hole in fragments, and so the bond between the bolt and the rock is destroyed.

At the basis of the invention is the technical problem of affording the most favorable conditions for fullling the purpose set out in the opening passage while employing an anchor with a plastic adhesive but without a cover plate.

These conditions, according to the invention, basically consist in:

3,430,449 Patented Mar. 4, 1969 (a) The annular clearance between the anchor bolt and the drill hole amounting to approximately 1.5 mm.;

(b) The anchor bolt being smooth in form and being provided with an unsymmetrical tip;

(c) The plastic component part of the mixtures being a low-viscosity polyester resin with a viscosity of the order of l0 poises;

(d) The plastic having added to it a finely granulated -filler in an amount in the ratio of the order of t0 400% of the weight of the plastic, the proportionate amount of filler being suited to the width of the annular clearance and being increased when the width of the latter is greater;

(e) The cartridge containing the plastic mixture and the hardener being formed with a thin wall.

After the plastic has hardened, in the annular clearance with its very small dimensions there cornes into existence a cylindrical body which consists of this material and which at its external periphery is inextricably and very effectively bonded to the friable rook, because the highviscosity plastics mixed with finely granulated filler penetrate particularly far into the cracks and crevices of the drill hole wall and fasten in the uneven places of the said hole. The arranging of a sufficient number of anchor drill holes filled in this manner, in a density matched to the circumstances of each individual case, so that the rock strata, cemented together to a certain degree, are converted in their totality into a self-supporting arch, is made possible by savings in drilling arising from the small annular clearance, the smooth anchor bolt and the highviscosity plastics mixed with finely granulated filler. The anchor bolt may therefore consist of various materials, even those having little mechanical stability, and may for example be formed as a thin-walled tube which, if so required, may be filled with a stifening substance, such as cement. In an extreme case, it is also conceivable that the bolt might consist of a still less stable material, such as wood or the like. It must merely be sufficiently compression-proof to allow of its being pressed into the supply of plastic material.

In order to achieve faultless filling of the narrow annular clearance with its relatively -great length, the driving in of the anchor bolt must be effectedin a rotary movement with a pressure greater than that exerted manually and at a high speed of rotation, the frictional heat engendered by this at one and the same time accelerating the hardening process of the plastic material.

On this point, it is preferable to work at a speed of the order of to 750 r.p.m. and at a mechanically exerted pressure of the order of 1 tonne.

The unsymmetrical tip of the anchor bolt improves the mixing effect and it can, for example, be formed as a wedge cut off on the slant or offset.

The cartridges containing the plastic and the hardener in separate compartments and employed in the new method for preference to bring the plastic into the furthest part of the drill hole consist of an easily destroyed material, for which, for example, even paper or cardboard may be considered. It has been shown to be particularly advantageous to employ cartridges of the type utilized in the adherent anchor method already known, these cartridges consisting of glass, because then the fragments arising through the shattering of the cartridge at the same time form constituent parts of the filler.

Corresponding effects can in given cases be achieved with cartridges or with inner containers (accommodated in them and holding the hardener) made of a flexible plastic material and provided with local weak spots distributed over their length which are destroyed at the commencement of pressure from the rotating rod and allow of the releasing of the component substances.

The drawing illustrates in individual phases the embodiment just described of the new method, and

FIGURE 1 shows the cartridge a inserted into the furthest part of a drill hole H and the anchor bolt b (in this case consisting of a tubular body filled with cement c), with the tip d, shaped as an unsymmetrical wedge, still at a distance from the cartridge;

FIGURE 2 shows the initial penetration of the anchor bolt b into the cartridge a and the resultant outflow of the plastic e, mixed with the hardener by the rotating head g of the bolt b, into the annular space between the bolt b and the drill hole Wall H; and

FIGURE 3 shows that the annualr space is iinally completely `filled with the cementing mixture and is blocked oli by a conically thickened formation on the end of the anchor bolt b.

This method is not, as regards its possibilities of application, confined to the consolidation of mine workings, but may be applied with advantage also in other cases in which the point at issue is the bonding of strata separate from each other or tending to crumble, for instance in general constructional work.

Below there is given an example of the carrying out of the new method, together with the gures involved.

lIn a roadway with a 12 m? internal section made through crumbly argillaceous schist, for every metre of the roadway two holes were drilled in the roof, with two holes to the right and two to the left, made diagonally into the upper portion of the area being worked. The length ofthe drill hole was 1.8 metres, the diameter of the drill hole was mm.

In each drill hole H a cartridge a of adhesive 22 mm. in diameter and 600 mm. long was inserted. The cartridge a was filled with a mixture of a reactive polyester resin and an inert iiller having a grain size of 0-1 mm. (pearl white) in the ratio of 123.5. In this mass there was an inner cartridge filled with benzoyl peroxide as a hardener, dispersed in gypsum for safety reasons. The inner cartridge was of approximately the same length as the outer cartridge and had a diameter of 6 mm.

After introducing the cartridge a into the drill hole H, the anchor bolt b was inserted in the drill hole at a rotational speed of about 600 r.p.m. and at a pressure of about 900 kg., a drill connected to the bolt head g being used to provide the drive. The bolt b consisted of a tube having an external diameter of 27 mm. and a wall thickness of 4.5 mm., its internal space being lilled with cement mortar c and its tip d being cut off on the slant.

Through inserting the bolt b, the cartridge a was completely destroyed and the mixture of polyester resin and iiller was for its part mixed with the benzoyl peroxide, the destroyed material of the cartridge being incorporated at the same time in the mass as a supplementary ller. After the bolt b had reached the furthest part of the drill hole H, the resulting mixture e completely illed the annular space between the bolt and the mouth of the drill hole and blocked oi by the conically thickened end g of the bolt.

After all the drill holes had been taken up in this manner and after a period of about minutes for hardening,

base-plates were screwed onto the bolts, without, however, bracing of the bolts being thereby brought about.

The success of the employment of the new consolidation method was shown by the fact that, whereas behind the area of the roadway safeguarded in this manner a section about 150 metres long became constricted by roof convergence to almost 1% of its internal section, in the area consolidated according to the invention no convergence or movements in the rock could be ascertained.

What we claim is:

1. Method for xing 4anchor bolts in drill holes, especially in friable rock, by means of a supply (positioned in the furthest part of the drill hole in a cartridge destroyed by the insertion of the anchor bolt) of a mixture of a plastic with a iller and an accelerator on the one hand and a hardener on the other hand, in separate compartments, characterized in that:

(a) the annular clearance between the anchor bolt and the drill hole amounts to approximately 1.5 mm.;

(b) the anchor bolt is smooth in form and is provided with an unsymmetrical tip;

(c) the plastic component part of the mixture comprises a low-viscosity polyester resin with a viscosity of the order of 10 poises;

(d) a finely granulated iiller added to said polyester resin in an amount in the ratio of the order of to 400% of the weight of the plastic, the proportionate amount of filler being suited to the width of the annular clearance and being increased when the width of the latter is greater;

(e) said drill hole is closed at its outer end by the conformation of the anchor bolt, and

(f) the positioning of the anchor bolt is effected at a rotational speed of the order of to 750 r.p.m. and at a mechanically exerted pressure of the order of about 900 kg.

2. An anchor bolt for use in drill holes formed in riable rock, comprising an elongate body of tubulaa form lled with a stiiienable material, the exterior surface of said body being smooth throughout its length, the diameter of said body being so chosen with respect to the drill hole intended for its reception as to provide a clearance of the order of 1.5 mm., an -unsymmetrical wedge-like tip on the inner end, and a conically thickened head closing the opposite end of said body.

References Cited UNITED STATES PATENTS 836,673 11/1906 Ford 52-725 1,971,051 8/1934 Reiner et al. 52--725 2,667,037 1/ 1954 Thomas et al 5,2-698 2,829,502 8/ 1958 Dempsey. 2,856,680 10/1958 Johnson et al. 3,108,443 10/ 1963 Schuermann et al. 3,302,410 2/1967 McLean.

EDWARD C. ALLEN, Primary Examiner.

U.S. Cl. X.R. 85--63 

